U.S. patent application number 17/123839 was filed with the patent office on 2021-07-01 for activated carbon fiber sheet for motor vehicle canister.
This patent application is currently assigned to NIPPON PAPER INDUSTRIES CO., LTD.. The applicant listed for this patent is NIPPON PAPER INDUSTRIES CO., LTD.. Invention is credited to Kenichi FUJINO, Daisuke IMAI, Shunsuke OZAWA, Yuu TAKATA, Yoshihide WATANABE, Chie YOSHIDA.
Application Number | 20210198111 17/123839 |
Document ID | / |
Family ID | 1000005473839 |
Filed Date | 2021-07-01 |
United States Patent
Application |
20210198111 |
Kind Code |
A1 |
IMAI; Daisuke ; et
al. |
July 1, 2021 |
ACTIVATED CARBON FIBER SHEET FOR MOTOR VEHICLE CANISTER
Abstract
An object of the present invention is to provide a new form of
adsorbent suitable for a motor vehicle canister. An activated
carbon fiber sheet satisfies one or two or more of conditions for
indices, such as a specific surface area, a pore volume of pores
having a given pore diameter, and a sheet density. An embodiment,
for example, may have: a specific surface area ranging from 1400 to
2200 m.sup.2/g; a pore volume ranging from 0.20 to 1.20 cm.sup.3/g
for pores having pore diameters of more than 0.7 nm and 2.0 nm or
less; and a sheet density ranging from 0.030 to 0.200
g/cm.sup.3.
Inventors: |
IMAI; Daisuke; (Tokyo,
JP) ; WATANABE; Yoshihide; (Tokyo, JP) ;
TAKATA; Yuu; (Tokyo, JP) ; OZAWA; Shunsuke;
(Tokyo, JP) ; YOSHIDA; Chie; (Tokyo, JP) ;
FUJINO; Kenichi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON PAPER INDUSTRIES CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
NIPPON PAPER INDUSTRIES CO.,
LTD.
Tokyo
JP
|
Family ID: |
1000005473839 |
Appl. No.: |
17/123839 |
Filed: |
December 16, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2019/022296 |
Jun 5, 2019 |
|
|
|
17123839 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01P 2006/14 20130101;
C01P 2006/12 20130101; F02M 25/0854 20130101; C01P 2006/16
20130101; C01B 32/318 20170801; C01P 2006/10 20130101 |
International
Class: |
C01B 32/318 20060101
C01B032/318; F02M 25/08 20060101 F02M025/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 19, 2018 |
JP |
2018-115823 |
Jan 24, 2019 |
JP |
2019-009959 |
Claims
1. An activated carbon fiber sheet for a motor vehicle canister,
comprising: a specific surface area ranging from 1400 to 2200
m.sup.2/g; a pore volume ranging from 0.20 to 1.20 cm.sup.3/g for
pores having pore diameters larger than 0.7 nm and equal to or
smaller than 2.0 nm; and a sheet density ranging from 0.030 to
0.200 g/cm.sup.3.
2. The activated carbon fiber sheet for a motor vehicle canister
according to claim 1, wherein a total pore volume of the activated
carbon fiber sheet ranges from 0.50 to 1.20 cm.sup.3/g.
3. The activated carbon fiber sheet for a motor vehicle canister
according to claim 1, wherein the activated carbon fiber sheet is a
carbonized product of cellulosic fiber.
4. The activated carbon fiber sheet for a motor vehicle canister
according to claim 1, wherein the activated carbon fiber sheet is
stored in the motor vehicle canister.
5. A motor vehicle canister, comprising: the activated carbon fiber
sheet for a motor vehicle canister according to claim 1.
6. A motor vehicle canister according to claim 5, wherein a total
pore volume of the activated carbon fiber sheet ranges from 0.50 to
1.20 cm.sup.3/g.
7. A motor vehicle canister according to claim 5, wherein the
activated carbon fiber sheet is a carbonized product of cellulosic
fiber.
8. A method of producing an activated carbon fiber sheet for a
motor vehicle canister, comprising: carbonizing and activating a
raw material sheet having one or both of a phosphoric acid-based
catalyst and an organic sulfonic acid-based catalyst; and
performing compaction such that the activated carbon fiber sheet
has a density ranging from 0.030 to 0.200 g/cm.sup.3.
9. A method of producing an activated carbon fiber sheet for a
motor vehicle canister according to claim 8, wherein the
carbonizing comprises heating treatment under an inert gas
atmosphere, the heating treatment being conducted for 30 minutes or
more including time for temperature to rise.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefits of
priorities from Japanese Patent Application No. 2018-115823, filed
Jun. 19, 2018; Japanese Patent Application No. 2019-009959, filed
Jan. 24, 2019; and International Application No. PCT/JP2019/022296,
filed Jun. 5, 2019, the entire contents of which are incorporated
herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to activated carbon fiber
sheets and particularly relates to activated carbon fiber sheets
suitable for use in motor vehicle canisters.
BACKGROUND ART
[0003] Gasoline-powered vehicles release fuel vapor that has filled
their fuel tanks due to change of pressure in the fuel tanks with
changes, such as changes in outside air temperature. The released
fuel vapor is considered to be one of substances causing PM2.5 or
photochemical smog. Canisters including adsorbents, such as
activated carbon, have been provided to prevent the release of the
fuel vapor into the atmosphere. (Hereinafter, in this Description,
a canister mounted in a motor vehicle may simply be referred to as
a "motor vehicle canister" or more simply a "canister.")
[0004] With the recent increase in awareness for environmental
conservation, gas emission regulations tend to be tightened year by
year, and there is thus a demand for canisters to have higher
adsorption performance. In addition, intake performance of motor
vehicles tends to be reduced due to the spread of systems including
start-stop systems, and gasoline adsorbed by adsorbents in their
canisters thus tends to be difficult to be desorbed. Therefore,
there is a demand for adsorbents used in canisters to have higher
performance. Activated carbon is used as an adsorbent used in
canisters, and has been proposed to be formed into granular shapes,
powdery shapes, or honeycomb shapes (for example, Patent Literature
1).
CITATION LIST
Patent Literature
[0005] Patent Literature 1: Japanese Patent Application Laid-open
No. 2013-173137
SUMMARY OF INVENTION
Technical Problem
[0006] Activated carbon fiber (or fibrous activated carbon) may be
referred to as the third activated carbon in contrast with
conventional powdered, granular, or pelletized activated carbon.
Activated carbon fiber is said to be relatively large in specific
surface area, large in adsorption capacity, and high in rate of
adsorption and desorption, among different forms of activated
carbon in a broad sense. However, activated carbon fiber has not
been put to practical use in canisters, and research and
development have not advanced sufficiently as to characteristics of
activated carbon fiber suitable for practical use in canisters.
[0007] In view of the foregoing, an object of the present invention
is to provide a new form of adsorbent suitable for motor vehicle
canisters.
Solution to Problem
[0008] Inventors of the present invention have conducted research
diligently and have found out that: in motor vehicle canisters,
adsorbents need to be fixed not to be worn away due to vibration,
for example; and a sheet formed of activated carbon fiber is
suitable for practical use in terms of ease of handling, for
example. However, the inventors have found out that demanded
performance per unit volume of a canister in a motor vehicle is
difficult to be achieved simply by placement of the activated
carbon fiber sheet in the housing of the canister, due to the
limited volume of the canister. As a result of further diligent
research, the inventors have found out that an activated carbon
fiber sheet suitable for motor vehicle canisters is able to be
provided by the following means, and have completed the present
invention.
[0009] [1] An activated carbon fiber sheet for a motor vehicle
canister, comprising:
[0010] a specific surface area ranging from 1400 to 2200
m.sup.2/g;
[0011] a pore volume ranging from 0.20 to 1.20 cm.sup.3/g for pores
having pore diameters larger than 0.7 nm and equal to or smaller
than 2.0 nm; and
[0012] a sheet density ranging from 0.030 to 0.200 g/cm.sup.3.
[0013] [2] The activated carbon fiber sheet for a motor vehicle
canister according to the above item [1], wherein a total pore
volume of the activated carbon fiber sheet ranges from 0.50 to 1.20
cm.sup.3/g.
[0014] [3] The activated carbon fiber sheet for a motor vehicle
canister according to the above item [1] or [2], wherein the
activated carbon fiber sheet is a carbonized product of cellulosic
fiber.
[0015] [4] A motor vehicle canister, comprising: the activated
carbon fiber sheet for a motor vehicle canister according to any
one of the above items [1] to [3].
[0016] [5] A method of producing an activated carbon fiber sheet
for a motor vehicle canister, comprising:
[0017] carbonizing and activating a raw material sheet holding one
or both of a phosphoric acid-based catalyst and an organic sulfonic
acid-based catalyst; and
[0018] performing compaction such that the activated carbon fiber
sheet has a density ranging from 0.030 to 0.200 g/cm.sup.3.
Advantageous Effects of Invention
[0019] The present invention enables provision of an activated
carbon fiber sheet that is easily handled, has high
adsorption-desorption performance for a low concentration, and is
suitable for canisters of motor vehicles.
[0020] Furthermore, the present invention enables provision of a
motor vehicle canister having excellent adsorption-desorption
performance for a low concentration.
DESCRIPTION OF EMBODIMENTS
[0021] Embodiments of the present invention will be described
hereinafter. Unless otherwise specified, the phrase "ranging from
AA to BB" means "being in the range of AA or more and BB or less"
(where "AA" and "BB" represent arbitrary numerical values).
[0022] 1. Activated Carbon Fiber Sheet for Motor Vehicle
Canisters
[0023] An activated carbon fiber sheet for a motor vehicle canister
of the present invention is a product in the form of a sheet made
of activated carbon fiber, and is suitably used as an adsorbent to
be stored in a canister mounted in a motor vehicle. (Hereinafter,
the activated carbon fiber sheet for a motor vehicle canister of
the present invention may simply be referred to as the activated
carbon fiber sheet of the present invention.) The activated carbon
fiber sheet of the present invention meets at least one condition
or any combination of two or more conditions of given conditions
described below.
[0024] Specific Surface Area
[0025] The lower limit of specific surface area of the activated
carbon fiber sheet of the present invention is preferably 1400
m.sup.2/g or more, more preferably 1500 m.sup.2/g or more, and even
more preferably 1600, 1700, or 1800 m.sup.2/g or more.
[0026] In general, while the activated carbon fiber sheet of the
present invention is preferably large in specific surface area in
terms of adsorption performance, the upper limit of specific
surface area for the activated carbon fiber sheet may be
approximately 2200 or 2000 m.sup.2/g or less.
[0027] Setting the specific surface area in the above range enables
the sheet to have more excellent adsorption-desorption performance
for fuel vapor.
[0028] Total Pore Volume
[0029] The lower limit of total pore volume of the activated carbon
fiber sheet of the present invention is preferably 0.50 cm.sup.3/g
or more, more preferably 0.60 cm.sup.3/g or more, and even more
preferably 0.70, 0.80, or 0.85 cm.sup.3/g or more.
[0030] The upper limit of total pore volume of the activated carbon
fiber sheet of the present invention is preferably 1.20 cm.sup.3/g
or less, more preferably 1.10 cm.sup.3/g or less, and even more
preferably 1.00 cm.sup.3/g or less.
[0031] Setting the total pore volume in the above range enables the
sheet to have more excellent adsorption-desorption performance for
fuel vapor.
[0032] Average Pore Diameter
[0033] The lower limit of average pore diameter of the activated
carbon fiber sheet of the present invention is preferably 1.69 nm
or more, more preferably 1.70 nm or more, and even more preferably
1.72, 1.75, 1.78, or 1.80 nm or more.
[0034] The upper limit of average pore diameter of the activated
carbon fiber sheet of the present invention may be arbitrary, but
is preferably 4.00 nm or less, more preferably 3.50 nm or less, and
even more preferably 3.00 nm or less.
[0035] Setting the average pore diameter in the above range enables
the sheet to have more excellent adsorption-desorption performance
for fuel vapor.
[0036] Ultramicropore Volume: V.sub.0.7
[0037] According to the present invention, the term
"ultramicropore" means a pore having a pore diameter of 0.7 nm or
less. (The term "pore diameter" means a diameter or width of a pore
and not a radius of the pore, unless otherwise specified.)
[0038] The lower limit of ultramicropore volume of the activated
carbon fiber sheet of the present invention is preferably 0.10
cm.sup.3/g or more, more preferably 0.20 cm.sup.3/g or more, and
even more preferably 0.22 or 0.25 cm.sup.3/g or more.
[0039] The upper limit of ultramicropore volume of the activated
carbon fiber sheet of the present invention is preferably 0.30
cm.sup.3/g or less, more preferably 0.29 cm.sup.3/g or less, and
even more preferably 0.28 or 0.27 cm.sup.3/g or less.
[0040] Setting the ultramicropore volume in the above range enables
the sheet to have more excellent adsorption-desorption performance
for fuel vapor.
[0041] Micropore Volume: V.sub.2.0
[0042] According to the present invention, the term "micropore"
means a pore having a pore diameter of 2.0 nm or less.
[0043] The lower limit of micropore volume of the activated carbon
fiber sheet of the present invention is preferably 0.45 cm.sup.3/g
or more, more preferably 0.50 cm.sup.3/g or more, and even more
preferably 0.55, 0.60, or 0.70 cm.sup.3/g or more.
[0044] The upper limit of micropore volume of the activated carbon
fiber sheet of the present invention is preferably 1.00 cm.sup.3/g
or less, more preferably 0.90 cm.sup.3/g or less, and even more
preferably 0.80 cm.sup.3/g or less.
[0045] Setting the micropore volume in the above range enables the
sheet to have more excellent adsorption-desorption performance for
fuel vapor.
[0046] Pore Volume of Pore Having Pore Diameter Larger than 0.7 nm
and Equal to or Less than 2.0 nm: V.sub.0.7-2.0
[0047] A pore volume V.sub.0.7-2.0 of pores having pore diameters
larger than 0.7 nm and equal to or smaller than 2.0 nm is able to
be determined by Equation 1 below using a value "a" of
ultramicropore volume and a value "b" of micropore volume.
V.sub.0.7-2.0=b-a (Equation 1)
[0048] The lower limit of the pore volume V.sub.0.7-2.0 of the
pores in the activated carbon fiber sheet of the present invention,
the pores having the pore diameters larger than 0.7 nm and 2.0 nm
or smaller, is preferably 0.20 cm.sup.3/g or more, more preferably
0.30 cm.sup.3/g or more, and even more preferably 0.36, 0.40, or
0.43 cm.sup.3/g or more.
[0049] The upper limit of the pore volume V.sub.0.7-2.0 of the
pores in the activated carbon fiber sheet of the present invention,
the pores having the pore diameters larger than 0.7 nm and equal to
or smaller than 2.0 nm, is preferably 1.20 cm.sup.3/g or less, more
preferably 1.00 cm.sup.3/g or less, and even more preferably 0.90,
0.80, 0.75, or 0.70 cm.sup.3/g or less.
[0050] Setting the pore volume V.sub.0.7-2.0 in the above range
enables the sheet to have more excellent adsorption-desorption
performance for fuel vapor.
[0051] Ratio of Volume of Ultramicropores to Volume of Micropores:
R.sub.0.7/2.0
[0052] A ratio R.sub.0.7/2.0 of the ultramicropores having pore
diameters of 0.7 nm or less to the pore volume of the micropores
having pore diameters of 2.0 nm or less is able to be determined by
Equation 2 below using a value "a" of the ultramicropore volume and
a value "b" of the micropore volume.
R.sub.0.7/2.0=a/b.times.100(%) (Equation 2)
[0053] In the activated carbon fiber sheet of the present
invention, the lower limit of the ratio R.sub.0.7/2.0 of the
ultramicropore volume to the micropore volume is preferably 25% or
more, more preferably 30% or more, and even more preferably 32% or
more.
[0054] In the activated carbon fiber sheet of the present
invention, the upper limit of the ratio R.sub.0.7/2.0 of the
ultramicropore volume to the micropore volume is preferably 60% or
less, more preferably 55% or less, and even more preferably 50, 45,
or 40% or less.
[0055] Setting the above-mentioned ultramicropores volume ratio
R.sub.0.7/2.0 in the above range enables the sheet to have more
excellent adsorption-desorption performance for fuel vapor.
[0056] Basis Weight (Weight Per Unit Area
[0057] The lower limit of basis weight of the activated carbon
fiber sheet of the present invention is preferably 30 g/m.sup.2 or
more, more preferably 35 g/m.sup.2 or more, and even more
preferably 37 or 40 g/m.sup.2 or more.
[0058] The upper limit of basis weight of the activated carbon
fiber sheet of the present invention is preferably 400 g/m.sup.2 or
less, more preferably 380 g/m.sup.2 or less, and even more
preferably 360, 350, 340, or 330 g/m.sup.2 or less.
[0059] Setting the basis weight in the above range enables the
sheet to have more excellent adsorption-desorption performance
demanded for use in the canister within a range of volume of
adsorbent that is able to be stored in the canister.
[0060] Sheet Thickness
[0061] The lower limit of sheet thickness of the activated carbon
fiber sheet of the present invention is preferably 0.3 mm or more,
more preferably 0.5 mm or more, and even more preferably 1.0 mm or
1.5 mm or more.
[0062] The upper limit of sheet thickness of the activated carbon
fiber sheet of the present invention is preferably 8.0 mm or less,
more preferably 7.0 mm or less, and even more preferably 4.0 mm or
3.0 mm or less.
[0063] Setting the sheet thickness in the above range enables the
sheet to have more excellent adsorption-desorption performance
demanded for use in the canister within a range of volume of
adsorbent that is able to be stored in the canister.
[0064] Sheet Density
[0065] The lower limit of density of the activated carbon fiber
sheet of the present invention is preferably 0.030 g/cm.sup.3 or
more, more preferably 0.035 g/cm.sup.3 or more, and even more
preferably 0.040 g/cm.sup.3 or more.
[0066] The upper limit of sheet density of the activated carbon
fiber sheet of the present invention is preferably 0.200 g/cm.sup.3
or less, more preferably 0.190 g/cm.sup.3 or less, and even more
preferably 0.180 or 0.170 g/cm.sup.3 or less.
[0067] Setting the sheet density in the above range enables the
sheet to have more excellent adsorption-desorption performance per
volume demanded for the canister within a range of volume of
adsorbent that is able to be stored in the canister.
[0068] Tensile Strength (MD: Machine Direction)
[0069] The lower limit of tensile strength (MD) of the activated
carbon fiber sheet of the present invention is preferably 0.05 kN/m
or more and more preferably 0.06 kN/m or more.
[0070] The upper limit of tensile strength (MD) of the activated
carbon fiber sheet of the present invention is not particularly
limited and may be arbitrary, and may be preferably 2.50 kN/m or
less, more preferably 2.40 kN/m or less, and even more preferably
2.30, 2.20, 2.10, or 2.00 kN/m or less.
[0071] Setting the tensile strength (MD) in the above range enables
the sheet to have flexibility. It is therefore possible to provide
an absorbent that has excellent workability, is difficult to be
damaged, and is able to be easily handled in operation including
placement of the adsorbent into a canister.
[0072] Tensile Strength (CD: Cross Direction)
[0073] The lower limit of tensile strength (CD) of the activated
carbon fiber sheet of the present invention is preferably 0.05 kN/m
or more, more preferably 0.06 kN/m or more, and even more
preferably 0.07 kN/m or more.
[0074] The upper limit of tensile strength (CD) of the activated
carbon fiber sheet of the present invention is not particularly
limited and may be arbitrary, and may be preferably 2.50 kN/m or
less, more preferably 2.40 kN/m or less, and even more preferably
2.30, 2.20, 2.10 or 2.00 kN/m or less.
[0075] Setting the tensile strength (CD) in the above range enables
the sheet to have flexibility. It is therefore possible to provide
an absorbent that has excellent workability, is resistant to
damage, and is able to be easily handled in operation including
placement of the adsorbent into a canister.
[0076] Moisture Content
[0077] The activated carbon fiber sheet of the present invention
preferably has a given moisture content. For example, the lower
limit of water content at 23.degree. C. and a relative humidity of
50% is preferably 1% or more, more preferably 2% or more, and even
more preferably 3% or more.
[0078] Furthermore, the upper limit of the water content at
23.degree. C. and a relative humidity of 50% is preferably 25% or
less, more preferably 22% or less, and even more preferably 15 or
10% or less.
[0079] Setting the water content in the above range under the above
conditions enables the sheet to be more excellent as an adsorbent
for motor vehicle canisters.
[0080] Methylene Blue Adsorption Performance
[0081] The activated carbon fiber sheet of the present invention
preferably has, as an adsorbent, given methylene blue adsorption
performance. The methylene blue absorption performance is able to
be represented as an amount of adsorbed methylene blue per
activated carbon fiber sheet weight. The methylene blue adsorption
performance of the activated carbon fiber sheet of the present
invention is preferably 60 ml/g or more, more preferably 70 ml/g or
more, and even more preferably 80, 90, or 100 ml/g.
[0082] Iodine Adsorption Performance
[0083] The activated carbon fiber sheet of the present invention
preferably has given iodine adsorption performance as an adsorbent.
The iodine absorption performance is able to be represented as an
amount of adsorbed iodine per activated carbon fiber sheet weight.
The iodine adsorption performance of the activated carbon fiber
sheet of the present invention is preferably 800 mg/g or more, more
preferably 900 mg/g or more, and even more preferably 1000, 1100,
or 1200 mg/g.
[0084] N-butane Adsorption-Desorption Performance
[0085] The activated carbon fiber sheet of the present invention
preferably has, as an adsorbent, given n-butane
adsorption-desorption performance. The n-butane
adsorption-desorption performance serves as an index of
adsorption-desorption performance for vapor; therefore, any
adsorbent having excellent n-butane adsorption-desorption
performance is suitable for use in motor vehicle canisters. The
n-butane adsorption-desorption performance is able to be
represented as an effective amount of adsorbed n-butane per
activated carbon fiber sheet weight. The effective amount of
adsorbed n-butane per activated carbon fiber sheet weight is an
amount of adsorbed n-butane in adsorption that is repeated
subsequently to desorption of n-butane from the adsorbent under
predetermined desorption conditions after sufficient absorption
breakthrough of n-butane on the adsorbent.
[0086] Preferred embodiments of the activated carbon fiber sheet of
the present invention may have an effective adsorption-desorption
amount of n-butane (an average of the second adsorption amount, the
second desorption amount, the third adsorption amount, and the
third desorption amount) that is preferably 0.380 mmol/g or more,
more preferably 0.420 mmol/g or more, and even more preferably
0.450, 0.500, or 0.550 mmol/g or more. The effective
adsorption-desorption amount of n-butane is determined according to
a measurement method described with respect to Examples below.
[0087] Furthermore, preferable embodiments of the activated carbon
fiber sheet of the present invention may have an effective
adsorption-desorption ratio of n-butane that is preferably 29.0% or
more, more preferably 31% or more, and even more preferably 32.0 or
34.0%. The effective adsorption-desorption ratio of n-butane is
determined according to a measurement method described with respect
to Examples below.
[0088] Combinations of Preferable Conditions
[0089] The activated carbon fiber sheet of the present invention
meets at least one or any combination of two or more of the
above-described conditions related to its physical properties or
performance. Preferred examples of these combinations will be
described below. The activated carbon fiber sheet of the present
invention is not limited to the following combinations.
[0090] Sheet of Embodiment 1
[0091] An activated carbon fiber sheet for a motor vehicle canister
satisfying the following conditions (1) to (3).
[0092] (1) Its specific surface area ranges from 1400 to 2200
m.sup.2/g.
[0093] (2) Its pore volume of pores having pore diameters larger
than 0.7 nm and equal to or smaller than 2.0 nm ranges from 0.20 to
1.20 cm.sup.3/g.
[0094] (3) Its sheet density ranges from 0.030 to 0.200
g/cm.sup.3.
[0095] Fuel vapor is a main target to be adsorbed onto the
adsorbent for motor vehicle canisters. The above-described specific
surface area and pore volume V.sub.0.7-2.0 are preferably satisfied
in terms of adsorption performance for fuel vapor.
[0096] Furthermore, motor vehicle canisters are limited in size and
the above-mentioned condition (3) related to the sheet density is
preferably satisfied for obtainment of the adsorbable amount by use
of the activated carbon fiber sheet. The activated carbon fiber
sheet may be formed by carbonization of a raw material that is a
fiber sheet and thus generally tends to be somewhat bulky and low
in density. In order to meet the above-mentioned condition (3), the
activated carbon fiber sheet is subjected to treatment, such as
pressure treatment, in its manufacturing process, to be
compacted.
[0097] As described above, the sheet of Embodiment 1 is in a
suitable form in terms of adsorption performance and adsorption
capacity demanded for motor vehicle canisters.
[0098] <Sheet of Embodiment 2>
[0099] An activated carbon fiber sheet for a motor vehicle canister
satisfying the following condition (4), in addition to the
conditions (1) to (3) according to the Embodiment 1.
[0100] (4) Its total pore volume is 0.50 to 1.20 cm.sup.3/g.
[0101] By satisfying the condition (4) as well as the conditions
(1) to (3), the sheet is even more preferable in terms of
obtainment of adsorption capacity demanded for the canister.
[0102] 2. Canister
[0103] The activated carbon fiber sheet of the present invention is
suitable as an adsorbent stored in a motor vehicle canister. That
is, the present invention enables provision of a motor vehicle
canister that is another embodiment.
[0104] The motor vehicle canister of the present invention has the
activated carbon fiber sheet as an adsorbent. The motor vehicle
canister has a structure that is not particularly limited, and may
have any general structure. For example, the motor vehicle canister
may be a motor vehicle canister having the following structure.
[0105] A canister including:
[0106] a housing;
[0107] an adsorbent chamber storing therein the adsorbent in the
housing;
[0108] a first inlet-outlet to connect between the adsorbent
chamber and an engine and allow gas to be sent into or sent out
from the adsorbent chamber;
[0109] a second inlet-outlet to connect between the adsorbent
chamber and a fuel tank and allow gas to be sent into or sent out
from the adsorbent chamber; and
[0110] a third inlet-outlet to open in response to application of a
given pressure to the third inlet-outlet from the adsorbent chamber
or from outside air, connect between the adsorbent chamber and the
outside air, and allow gas to be sent into or release from the
adsorbent chamber.
[0111] The arrangement of these inlet-outlets is not particularly
limited, but the third inlet-outlet is preferably placed at a
position enabling gas to sufficiently pass through the adsorbent
when the gas moves between: the third inlet-outlet and the first or
second inlet-outlet. For example, according to one embodiment, the
first and second inlet-outlets may be provided on a first side face
of the housing and the third inlet-outlet may be provided on a
second side face thereof located opposite to the first side
face.
[0112] The adsorbent chamber may have more than one room. For
example, the adsorbent chamber may be divided into two or more
sections by partition walls. The partition walls to be used may be
porous plates having gas permeability. Furthermore, an additional
adsorbent room may be equipped by provision of an external second
housing separately from the first housing so that the first and the
second housings are connected to each other via a gas passage. If
plural sections or housings are provided as described above,
according to a preferred embodiment, the adsorbent or the adsorbent
chamber may be provided so that adsorption capacities in these
sections or housings decrease one by one from the direction of an
inlet-outlet for fuel vapor (the direction of the first
inlet-outlet) to the direction of an outside air opening (the
direction of the second inlet-outlet). Specifically, for example,
according to this preferred embodiment, a composite canister may
have a main canister (a first housing) and a second canister (a
second housing) that is additionally provided to the main canister
and is nearer to the outside air opening than the main canister is.
A high performance canister is able to be provided with reduced
cost when plural sections or housings are provided as described
above, the high performance canister having: a main body (a first
section or a first housing) with the largest storage capacity; and
a second or later section or housing with a relatively smaller
storage capacity. This main body is a section or housing nearest to
an inlet-outlet for fuel vapor and stores therein conventional and
lower-cost activated carbon. The second or later section or housing
stores therein the active carbon fiber sheet of the present
invention which has excellent adsorption-desorption performance for
a low concentration.
[0113] When there is more than one adsorbent chamber, fuel vapor
flowing, from a preceding layer, into an adsorbent chamber nearer
to the outside air opening has become lower in concentration.
Therefore, the activated carbon fiber sheet of the present
invention, which has high n-butane adsorption performance for a low
concentration of about 0.2%, is suitable as an adsorbent to be
stored in a second or later section or housing located nearer to
the outside air opening.
[0114] In the case where the activated carbon fiber sheet of the
present invention is used in the adsorbent chamber nearer to the
outside air opening, the amount of leakage of fuel vapor upon
stoppage of the motor vehicle for a long time is able to be reduced
since the effective amount of adsorption-desorption by the
activated carbon fiber sheet of the present invention through
purging thereof is large. The activated carbon fiber sheet of the
present invention is thus also suitable as an adsorbent to be used
in a motor vehicle canister.
[0115] Therefore, preferred embodiments of the canister include,
for example, the following embodiments.
[0116] A motor vehicle canister comprising two or more adsorbent
chambers,
[0117] wherein a second or subsequent adsorbent chamber/chambers
provided nearer to an outside air opening than a first adsorbent
chamber provided nearest to a fuel vapor inlet-outlet stores/store
therein the activated carbon fiber sheet of the present
invention.
[0118] Furthermore, according to a preferred embodiment, the active
carbon fiber sheet may serve as an active carbon fiber sheet for
the second or subsequent adsorbent chamber/chambers in the motor
vehicle canister having the two or more adsorbent chambers.
[0119] In the above embodiments, the number of the adsorbent
chambers may be two or more. If the number of the adsorbent
chambers is three or more, the activated carbon fiber sheet of the
present invention may be stored in at least one of these adsorbent
chambers that is after the second adsorbent chamber.
[0120] 3. Method of Manufacturing Activated Carbon Fiber Sheet
[0121] The above-described activated carbon fiber sheet of the
present invention is manufactured so as to satisfy conditions
selected from the above-described given conditions. The activated
carbon fiber sheet of the present invention is able to be made, for
example, as follows.
[0122] One preferred embodiment of a method of manufacturing the
activated carbon fiber sheet of the present invention (hereinafter,
referred to as "Embodiment 1 of manufacturing method")
includes:
[0123] carbonizing and activating a raw material sheet holding one
or both of a phosphoric acid-based catalyst and an organic sulfonic
acid-based catalyst; and
[0124] performing pressure treatment so that the activated carbon
fiber sheet has a density of 0.030 to 0.200 g/cm.sup.3.
[0125] 3-1. Preparation of Raw Material Sheet (Precursor)
[0126] Type of Fiber
[0127] Examples of fiber forming the raw material sheet include
cellulosic fiber, pitch-based fiber, PAN-based fiber, phenol
resin-based fiber, and preferably include cellulosic fiber.
[0128] Cellulosic Fiber
[0129] The cellulosic fiber refers to fiber composed mainly of
cellulose and/or a derivative thereof. Origins of cellulose and
cellulose derivatives may be any one or more of examples including
chemically synthesized products, plant derived cellulose,
regenerated cellulose, and cellulose produced by bacteria. Examples
of the cellulosic fiber preferably used include fiber formed of a
plant cellulose material obtained from plants, such as trees, and
fiber formed of a long fibrous regenerated cellulose material
obtained by dissolution of a plant cellulose material (such as
cotton or pulp) through chemical treatment. In addition, the fiber
may contain components, such as lignin and/or hemicellulose.
[0130] Examples of raw materials for the cellulosic fiber (the
plant cellulose material or regenerated cellulose material) may
include: plant cellulose fiber, such as cotton (such as short fiber
cotton, medium fiber cotton, long fiber cotton, super long cotton,
and ultra super long cotton), hemp, bamboo, kozo, mitsumata,
banana, and tunicates; regenerated cellulose fiber, such as
cuprammonium rayon, viscose rayon, polynosic rayon, and cellulose
made from bamboo; purified cellulose fiber spun by use of organic
solvent (N-methylmorpholine N-oxide); and acetate fiber, such as
diacetate and triacetate. In terms of availability, a preferred one
or preferred ones of these examples is/are at least one selected
from cuprammonium rayon, viscose rayon, and purified cellulose
fiber.
[0131] Diameters of monofilaments forming the cellulosic fiber
range from 5 to 75 .mu.m, and the density of the monofilaments
ranges from 1.4 to 1.9 m.sup.3/g.
[0132] Embodiments of the cellulosic fiber are not particularly
limited, and according to purposes, the cellulosic fiber prepared
into a form, such as raw yarn (unprocessed yarn), false twisted
yarn, dyed yarn, single yarn, folded yarn, or covering yarn, may be
used. When the cellulosic fiber includes two or more kinds of raw
materials, the cellulosic fiber may be, for example, blended yarn
or blended twisted yarn. Furthermore, the above-mentioned raw
materials in various forms may be used alone or in combination of
two or more as the cellulosic fiber. Non-twisted yarn is preferred
among the above-mentioned raw materials for both moldability and
mechanical strength of the composite material.
[0133] Fiber Sheet
[0134] A fiber sheet refers to a sheet obtained by processing of a
large number of filaments of fiber into a thin and wide sheet.
Fiber sheets include woven fabric, knitted fabric, and nonwoven
fabric.
[0135] Methods of weaving the cellulosic fiber are not particularly
limited, and a general method can be used. Weaves of the woven
fabric are not particularly limited either, and any of three
foundation weaves, a plain weave, a twill weave, or a satin weave,
may be used.
[0136] Gaps between warp yarns and between weft yarns of the
cellulosic fiber in the woven fabric formed of the cellulosic fiber
range preferably from 0.1 to 0.8 mm, more preferably from 0.2 to
0.6 mm, and even more preferably from 0.25 to 0.5 mm. Furthermore,
the woven fabric formed of the cellulosic fiber has a mass per unit
area ranging preferably from 50 to 500 g/m.sup.2 and more
preferably from 100 to 400 g/m.sup.2.
[0137] Setting the gaps and the mass per unit area of the
cellulosic fiber and the woven fabric formed of the cellulosic
fiber in the above ranges enables carbon fiber woven fabric
obtained by heat treatment of the woven fabric to have excellent
strength.
[0138] Methods of manufacturing the nonwoven fabric are also not
particularly limited. Examples of the methods may include: a method
where a fiber sheet is obtained by use of a dry method or a wet
method with the above-mentioned fiber serving as a raw material and
having been cut into appropriate lengths; and a method where a
fiber sheet is directly obtained from a solution by use of an
electrospinning method. After the nonwoven fabric is obtained,
treatment, such as resin bonding, thermal bonding, spun lacing, or
needle punching, may be added for the purpose of bonding the
filaments of fiber together.
[0139] 3-2. Catalyst
[0140] According to Embodiment 1 of manufacturing method, a
catalyst is held by the raw material sheet prepared as described
above. The raw material sheet holding the catalyst is carbonized
and further activated by using gas, such as steam, carbon dioxide,
or air gas, and a porous activated carbon fiber sheet is thus able
to be obtained. Examples of the catalyst that may be used include a
phosphoric acid-based catalyst and an organic sulfonic acid-based
catalyst.
[0141] Phosphoric Acid-based Catalyst
[0142] Examples of the phosphoric acid-based catalyst may include:
oxyacids of phosphorus, such as phosphoric acid, metaphosphoric
acid, pyrophosphoric acid, phosphorous acid, phosphoric acid,
phosphorous acid, and phosphinic acid;
[0143] ammonium dihydrogen phosphate, diammonium hydrogen
phosphate, triammonium phosphate, dimethyl phosphono propanamide,
ammonium polyphosphate, and polyphosphonitrile chloride; and
condensation products between: phosphoric acid, tetrakis
(hydroxymethyl) phosphonium salt, or tris (1-aziridinyl) phosphine
oxide; and urea, thiourea, melamine, guanine, cyanamide, hydrazine,
dicyandiamide, or a methylol derivative of any one of these.
Preferable examples may include diammonium hydrogen phosphate. One
kind of phosphoric acid-based catalysts may be used alone or two or
more kinds of phosphoric acid-based catalysts may be used in
combination. When the phosphoric acid-based catalyst is used in the
form of an aqueous solution, the phosphoric acid-based catalyst in
the aqueous solution has a concentration ranging preferably from
0.05 to 2.0 mol/L and more preferably from 0.1 to 1.0 mol/L.
[0144] Organic Sulfonic Acid-based Catalyst
[0145] An organic compound having one or more sulfo groups can be
used as the organic sulfonic acid. For example, a compound in which
a sulfo group is bonded to any of various carbon skeletons of
aliphatic series or aromatic series can be used. A preferred
organic sulfonic acid-based catalyst has a low molecular weight in
terms of handling of the catalyst.
[0146] Examples of the organic sulfonic acid-based catalyst may
include compounds represented by R--SO.sub.3H where: R is a linear
or branched alkyl group having 1 to 20 carbon atoms, a cycloalkyl
group having 3 to 20 carbon atoms, or an aryl group having 6 to 20
carbon atoms; and each of the alkyl group, the cycloalkyl group and
the aryl group optionally has a substituent of an alkyl group, a
hydroxyl group, or a halogen group. Examples of the organic
sulfonic acid-based catalyst may include methanesulfonic acid,
ethanesulfonic acid, propanesulfonic acid, 1-hexanesulfonic acid,
vinylsulfonic acid, cyclohexanesulfonic acid, p-toluenesulfonic
acid, p-phenolsulfonic acid, naphthalenesulfonic acid,
benzenesulfonic acid, and camphorsulfonic acid. Methanesulfonic
acid may be preferably used among these examples. One kind of these
organic sulfonic acid-based catalysts may be used alone, or two or
more kinds of these organic sulfonic acid-based catalysts may be
used in combination.
[0147] When the organic sulfonic acid is used in the form of an
aqueous solution, the organic sulfonic acid in the aqueous solution
has a concentration ranging preferably from 0.05 to 2.0 mol/L and
more preferably from 0.1 to 1.0 mol/L.
[0148] Mixed Catalyst
[0149] The above-mentioned phosphoric acid-based catalyst and
organic sulfonic acid-based catalyst may be mixed and used as a
mixed catalyst. The mixing ratio may be adjusted as
appropriate.
[0150] Holding of Catalyst
[0151] The catalyst is held by the raw material sheet. "Being held"
means that the catalyst is kept in contact with the raw material
sheet, and the catalyst may be held in various forms through, for
example, adhesion, adsorption, or impregnation. Methods for the
catalyst to be held by the raw material sheet are not particularly
limited and include, for example, a method of immersing the raw
material sheet in an aqueous solution containing the catalyst, a
method of sprinkling an aqueous solution containing the catalyst
over the raw material sheet, a method of causing the raw material
sheet to be in contact with vapor that is the catalyst that has
been vaporized, and a method of mixing the fiber of the raw
material sheet into an aqueous solution containing the catalyst to
make paper.
[0152] A method that can be preferably used for sufficient
carbonization is a method of immersing the raw material sheet in an
aqueous solution containing the catalyst to impregnate the fiber
with the catalyst such that the catalyst reaches the inside of the
fiber. The temperature for the immersion in the aqueous solution
containing the catalyst is not particularly limited and may
preferably be room temperature. The immersion time ranges
preferably from 10 seconds to 120 minutes and more preferably from
20 seconds to 30 minutes. The immersion allows the fiber forming
the raw material sheet to adsorb, for example, 1 to 150% by mass
and preferably 5 to 60% by mass, of the catalyst. After the
immersion, the raw material sheet is preferably taken out from the
aqueous solution and dried. A method of drying the raw material
sheet may be, for example, any of methods including a method of
leaving the raw material sheet at room temperature or putting the
raw material sheet in a dryer. The drying may be performed until
the sample no longer changes in weight by evaporation of excess
moisture after the sample is removed from the aqueous solution
containing the catalyst. For example, in the drying at room
temperature, the drying time for which the raw material sheet is
left may be 0.5 days or more. When the raw material sheet holding
the catalyst almost no longer changes in mass because of the
drying, the raw material sheet holding the catalyst proceeds to the
step to be carbonized.
[0153] 3-3. Carbonization Treatment
[0154] After being prepared, the raw material sheet holding the
catalyst is subjected to carbonization treatment. The carbonization
treatment for obtainment of the activated carbon fiber sheet may be
performed according to a general method of carbonizing activated
carbon. The carbonization treatment according to a preferred
embodiment may be performed as follows.
[0155] The carbonization treatment is usually performed under an
inert gas atmosphere. According to the present invention, the inert
gas atmosphere means an oxygen-free or low-oxygen atmosphere in
which carbon is difficult to undergo a combustion reaction and is
thus carbonized. The inert gas atmosphere may preferably be an
atmosphere including gas, such as argon gas or nitrogen gas.
[0156] The raw material sheet holding the catalyst is subjected to
heat treatment and carbonized in the given gas atmosphere mentioned
above.
[0157] The lower limit of the heating temperature is preferably
300.degree. C. or higher, more preferably 350.degree. C. or higher,
and even more preferably 400.degree. C. or higher or 750.degree. C.
or higher.
[0158] The upper limit of the heating temperature is preferably
1400.degree. C. or lower, more preferably 1300.degree. C. or lower,
and even more preferably 1200.degree. C. or lower or 1000.degree.
C. or lower.
[0159] Setting the heating temperature as described above enables
obtainment of a carbon fiber sheet with its fiber form maintained.
If the heating temperature is lower than the above-mentioned lower
limit, the carbon fiber may have a carbon content of 80% or less
and carbonization may thus be insufficient.
[0160] The lower limit of the heat treatment time including the
time for the temperature to rise is preferably 10 minutes or more,
more preferably 11 minutes or more, even more preferably 12 minutes
or more, and still even more preferably 30 minutes or more.
[0161] The upper limit of the heat treatment time may be optional,
but is preferably 180 minutes or less, more preferably 160 minutes,
and even more preferably 140 minutes or less.
[0162] By sufficiently impregnating the raw material sheet with the
catalyst, setting the above-mentioned suitable heating temperature,
and adjusting the heat treatment time, it is possible to adjust the
degree of progress of pore formation and thus adjust the physical
properties of the porous body, such as the specific surface area,
the volume of the various pores, and the average pore diameter.
[0163] If the heat treatment time is shorter than the above lower
limit, carbonization tends to be insufficient.
[0164] Furthermore, the heat treatment can include further
reheating treatment under a given gas atmosphere after the
above-described heat treatment (which may be referred to as primary
heat treatment). That is, the carbonization treatment may be
performed by dividing the heat treatment into two or more stages
having different conditions, such as different temperatures. By
performing the primary heat treatment and the reheating treatment
under predetermined conditions, it may be possible to adjust the
physical properties, promote the carbonization and the subsequent
activation, and thus obtain an activated carbon fiber sheet having
excellent adsorption and desorption properties.
[0165] 3-4. Activation Treatment
[0166] The activation treatment according to the present invention
may be, for example, performed continuously after the
above-described heat treatment, by providing steam and keeping an
appropriate activation temperature for a predetermined time, and
the activated carbon fiber sheet is thereby able to be
obtained.
[0167] The lower limit of the activation temperature is preferably
300.degree. C. or higher, more preferably 350.degree. C. or higher,
and even more preferably 400 or 750.degree. C. or higher.
[0168] On the other hand, the upper limit of the activation
temperature is preferably 1400.degree. C. or lower, more preferably
1300.degree. C. or lower, and even more preferably 1200 or
1000.degree. C. or lower.
[0169] When the activation treatment is performed continuously
after the heat treatment, the activation temperature is preferably
adjusted to a temperature that is almost the same as the heating
temperature.
[0170] The lower limit of the activation time is preferably one
minute or more, and more preferably five minutes or more.
[0171] The upper limit of the activation time may be optional, but
is preferably 180 minutes or less, more preferably 160 minutes or
less, and even more preferably 140 minutes or less, 100 minutes or
less, 50 minutes or less, or 30 minutes or less.
[0172] 3-5. Compaction
[0173] The activated carbon fiber sheet of the present invention
preferably has a sheet density that has been adjusted. Compaction
is preferably performed at any stage of the manufacturing process.
The compaction may be performed, for example, by applying pressure
to the sheet to increase the density.
[0174] Examples of embodiments of the compaction may include the
following four types.
(1) A raw material sheet containing a binder, such as a resin, is
subjected to heating and pressurization treatment, and the raw
material sheet increased in density is thereby prepared and is then
subjected to carbonization treatment. (2) In a step of performing
carbonization treatment, a sheet is subjected to pressurization
treatment while carbonization is being performed. (3) After
carbonization treatment, a binder, such as resin, is added to an
activated carbon fiber sheet and the activated carbon fiber sheet
is then subjected to heating and pressurization treatment. (4) An
activated carbon fiber sheet is defibrated and then mixed with pulp
or the like.
EXAMPLES
[0175] Hereinafter, the present invention will be described more
specifically with reference to examples, but the technical scope of
the present invention is not limited to the following examples.
[0176] Various items related to physical properties and performance
of activated carbon fiber sheets and granular activated carbon were
measured and evaluated by methods described below. Various
numerical values defining the present invention are able to be
determined by the following measurement methods and evaluation
methods.
[0177] Specific Surface Area
[0178] About 30 mg of an activated carbon fiber sheet were
collected, vacuum-dried at 200.degree. C. for 20 hours, weighed,
and measured using a high-precision gas/vapor adsorption amount
measuring apparatus BELSORP-MAX II (MicrotracBEL Corp.). The
adsorption amount of nitrogen gas at the boiling point of liquid
nitrogen (77 K) was measured at a relative pressure ranging from
the 10.sup.-8 order to 0.990, and an adsorption isotherm of the
sample was thereby prepared. This adsorption isotherm was analyzed
by the BET method for which the relative pressure range for
analysis had been automatically determined under the conditions of
the adsorption isotherm of Type I (ISO 9277), and the BET specific
surface area per weight (unit: m.sup.2/g) was determined as a
specific surface area (unit: m.sup.2/g).
[0179] Total Pore Volume
[0180] The total pore volume (unit: cm.sup.3/g) by a one-point
method was calculated based on the result at the relative pressure
of 0.990 on the adsorption isotherm obtained according to the above
description related to the specific surface area.
[0181] Average Pore Diameter
[0182] Calculation was performed by use of Equation 3 below.
Average pore diameter (unit: nm)=4.times.total pore
volume.times.10.sup.3 specific surface area (Equation 3)
[0183] Ultramicropore Volume
[0184] The adsorption isotherm obtained according to the above
description related to the specific surface area was analyzed using
the analysis software BELMaster pertaining to the high-precision
gas/vapor adsorption amount measuring apparatus BELSORP-MAX II
(MicrotracBEL Corp.) through the GCMC method with the analysis
settings set as follows: "Smoothing (moving average processing
using one point each before and after every analyzed point of the
pore distribution)," "Distribution function: No-assumption,"
"Definition of pore diameter: Solid and Fluid Def. Pore Size," and
"Kernel: Slit-C-Adsorption." The integrated pore volume at 0.7 nm
was read from the obtained pore distribution curve for adsorption,
the integrated pore volume serving as the ultramicropore volume
(unit: cm.sup.3/g).
[0185] Micropore Volume
[0186] The adsorption isotherm obtained according to the above
description related to the specific surface area was analyzed using
the analysis software BELMaster pertaining to the high-precision
gas/vapor adsorption amount measuring apparatus BELSORP-MAX II
(MicrotracBEL Corp.) through the GCMC method with the analysis
settings set as follows: "Smoothing (moving average processing
using one point each before and after every analyzed point of the
pore distribution)," "Distribution function: No-assumption,"
"Definition of pore diameter: Solid and Fluid Def. Pore Size," and
"Kernel: Slit-C-Adsorption." The integrated pore volume at 2.0 nm
was read from the obtained pore distribution curve for adsorption,
the integrated pore volume serving as the micropore volume (unit:
cm.sup.3/g).
[0187] Basis Weight of Sheet
[0188] After the activated carbon fiber sheet was allowed to stand
for 12 hours or more under the environment where the temperature
was 23.+-.2.degree. C. and the relative humidity was 50.+-.5%, the
basis weight (unit: g/m.sup.2) of the sheet was determined from the
weight and the lengthwise and widthwise dimensions of the
sheet.
[0189] Thickness of Sheet
[0190] The activated carbon fiber sheet was allowed to stand for 12
hours or more under the environment where the temperature was
23.+-.2.degree. C. and the relative humidity was 50.+-.5%, and the
thickness of the sheet was then measured by use of a small digital
thickness measuring device FS-60DS (Daiei Kagaku Seiki Mfg. Co.,
Ltd.) with a load of 0.3 KPa applied to the sheet.
[0191] Density of Sheet
[0192] Calculation was performed by use of Equation 4 below.
Density of sheet (unit: g/cm.sup.3)=basis weight of sheet/thickness
of sheet/10.sup.3 (Equation 4)
[0193] Tensile Strength (MD), Tensile Strength (CD), Elongation
Percentage (MD), and Elongation Percentage (CD)
[0194] The activated carbon fiber sheet was allowed to stand for 12
hours or more under the environment where the temperature was
23.+-.2.degree. C. and the relative humidity was 50.+-.5%. Test
pieces (each with a width of 15 mm and a length 50 to 60 mm) were
then cut out from the sheet along Machine Direction (MD) or Cross
Direction (CD) orthogonal to Machine Direction (MD) so that lengths
of the test pieces were respectively along Machine Direction and
along Cross Direction. Using a Tensilon universal testing
instrument RTG-1210 (A & D Co. Ltd.), the test pieces were
pulled with the length between grips at 40 mm and the pulling speed
at 100 mm/min. The tensile strength and elongation percentage were
respectively calculated by Equations 5 and 6 below.
Tensile strength (unit: kN/m)=maximum load (unit: N) applied during
test/15 mm Equation 5
Elongation percentage (unit: %)=amount of elongation at maximum
load (unit: mm)/40 mm Equation 6
[0195] Moisture Content
[0196] The activated carbon fiber sheet was allowed to stand for 12
hours or more under the environment where the temperature was
23.+-.2.degree. C. and the relative humidity was 50.+-.5%, a sample
of 0.5 to 1.0 g was thereafter collected from the sheet and dried
at 115.+-.5.degree. C. for three hours or more in a dryer, and
moisture (unit: %) was determined from change in weight of the
dried sample.
[0197] Methylene Blue Adsorption Performance
[0198] Measurement according to methylene blue decolorizing power
(unit: ml/g) of powdered activated carbon for water supply
conforming to Japan Water Works Association standards (JWWA K113)
was performed, and results of the measurement were determined as
the methylene blue adsorption performance (unit: ml/g).
[0199] Iodine Adsorption Performance
[0200] Measurement was performed according to iodine adsorption
performance (unit: mg/g) of powdered activated carbon for water
supply conforming to Japan Water Works Association standards (JWWA
K113).
[0201] N-Butane Adsorption-Desorption Performance
[0202] A sample of 0.114 cm.sup.3 was collected from the activated
carbon fiber sheet and was subjected to measurement using a
catalyst analyzer BELCAT II (MicrotracBEL Corp.). At a test
temperature of 25.degree. C., normal butane gas diluted to a
concentration of 0.2% with nitrogen gas was allowed to pass through
the sample at 50 cm.sup.3/min so that adsorption breakthrough of
n-butane on the sample was reached, and then desorption of n-butane
was performed by allowing nitrogen gas at 23 cm.sup.3/min to pass
through the sample for about 600 seconds such that the volume of
nitrogen gas passed reached 2,000 times the volume of the activated
carbon fiber sheet. This adsorption-desorption process was repeated
three times. The average of the second adsorption amount, the
second desorption amount, the third adsorption amount, and the
third desorption amount was determined as the effective
adsorption-desorption amount (mmol/g). The effective
adsorption-desorption ratio (%) was determined by dividing the
effective adsorption-desorption amount by the first adsorption
amount.
Example 1
[0203] A needle-punched nonwoven fabric made of rayon fiber (at 1.7
dtex, having a fiber length of 40 mm) and having a basis weight of
300 g/m.sup.2 was impregnated with 5 to 8% diammonium hydrogen
phosphate aqueous solution, wrung out, and dried, to have 8 to 10%
by weight of diammonium hydrogen phosphate attached to the nonwoven
fabric. The obtained pretreated nonwoven fabric was heated in a
nitrogen atmosphere to 900.degree. C. in 50 minutes while being
pressurized, and was kept at this temperature for 4 minutes.
Continuously at that temperature, activation treatment was
performed for 10 minutes in a nitrogen gas stream containing steam
with a dew point of 60.degree. C.
Example 2
[0204] A needle-punched nonwoven fabric made of rayon fiber (at 3.3
dtex, having a fiber length of 76 mm) and having a basis weight of
300 g/m.sup.2 was impregnated with 5 to 8% diammonium hydrogen
phosphate aqueous solution, wrung out, and dried, to have 8 to 10%
by weight of diammonium hydrogen phosphate attached to the nonwoven
fabric. The obtained pretreated nonwoven fabric was heated in a
nitrogen atmosphere to 900.degree. C. in 50 minutes, and was kept
at this temperature for 12 minutes. Continuously at that
temperature, activation treatment was performed for 10 minutes in a
nitrogen gas stream containing steam with a dew point of 60.degree.
C.
Example 3
[0205] An activated carbon fiber sheet of Example 3 was prepared in
the same manner as that in Example 2, except that the activation
treatment time in Example 2 was changed to 23 minutes.
Comparative Example 1
[0206] An activated carbon fiber sheet of Comparative Example 1 was
prepared in the same manner as that in Example 2, except that the
temperature rising time to 900.degree. C. was changed to 25
minutes, the time in which the temperature was kept at 900.degree.
C. was changed to 2 minutes, and the activation treatment time was
changed to 6 minutes, from those in Example 2.
Comparative Example 2: Granular Activated Carbon
[0207] Granular activated carbon filling a commercially available
canister was taken out and used as an adsorbent of Comparative
Example 2.
[0208] The commercially available canister used was a canister
having a product number of 77740-48220 (by Toyota Yamaguchi Parts
Distributor Co., Ltd.).
[0209] Results of measurement of physical properties and
performance for Examples 1 to 3 and Comparative Examples 1 and 2
are listed in Table 1.
TABLE-US-00001 TABLE 1 Measurement Results Examp- Exam- Exam-
Comparative Comparative le 1 ple 2 ple 3 Example 1 Example 2
Granular activated Reference carbon for Standards or ACF ACF ACF
ACF canister Analysis Method Precursor Rayon fiber Rayon fiber
Rayon fiber -- 1.7 dtex, 3.3 dtex, 3.3 dtex, 40 mm 76 mm 76 mm
N.sub.2 adsorption Specific surface area m.sup.2/g 1480 1720 1980
1160 1640 JIS K 1477 BET analysis Total pore volume cm.sup.3/g 0.64
0.75 0.91 0.49 1.29 Basic physical properties Average pore diameter
nm 1.72 1.73 1.84 1.68 3.14 related to adsorption performance
N.sub.2 adsorption a) Ultramicropore cm.sup.3/g 0.26 0.24 0.26 0.33
0.09 Simulation analysis: GCMC volume.sup.1) Grand Canonical Monte
analysis b) Micropore volume.sup.2) cm.sup.3/g 0.58 0.65 0.75 0.47
0.44 Carlo Method b)-a) cm.sup.3/g 0.33 0.41 0.49 0.15 0.35 a)/b))
% 44 37 35 69 20 Sheet Physical Basis Weight g/m.sup.2 127 133 90
198 -- Property Thickness mm 1.0 2.3 2.2 2.5 -- Density g/cm.sup.3
0.126 0.057 0.041 0.079 0.26 Sheet Physical Tensile strength MD
kN/m 0.20 0.16 0.13 0.17 -- Property Tensile strength CD 0.22 0.14
0.16 0.17 -- Moisture (23.degree. C., 50% RH) % 14 6 4 27 11 JIS K
1477 Methylene blue adsorption performance ml/g 160 270 330 80 0 to
10 JIS K 1477, JWWA K 113 Iodine adsorption performance mg/g 1300
1600 1700 1100 710 JIS K 1477, JWWA K 113 0.2% First adsorption
amount mmol/g 1.619 1.716 1.803 1.373 0.749 n-butane Effective
adsorption- 0.571 0.663 0.752 0.413 0.211 adsorption- desorption
desorption amount.sup.3) (Average of performance second and third)
Effective adsorption- 35.3 38.6 41.7 30.1 28.2 desorption
ratio.sup.4) .sup.1)Pore diameter is 0.7 nm or less. .sup.2)Pore
diameter is 2.0 nm or less. .sup.3)Average of 2nd adsorption
amount, 2nd desorption amount, 3rd adsorption amount, and 3rd
desorption amount .sup.4)(Effective adsorption-desorption
arnount/first adsorption amount) .times. 100 (%)
[0210] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *